Identification of inflammatory cells in developing rat periapical lesions

Impact of endodontic and periodontal diseases and treatments on the aorta and liver of obese and non-obese rats

AIM

To evaluate the impact of the presence and treatment of periodontal disease (PD) and apical periodontitis (AP) on the aorta and liver of obese and non-obese rats.

METHODOLOGY

One hundred and forty Wistar rats were divided into two groups, according to the diet administered: normal diet (-n), without obesity; and cafeteria diet (-c), with induced obesity. These groups were divided into seven subgroups according to the specific experimental protocols: naïve control (NC); AP; AP with treatment (APt); PD; PE with treatment (PDt); AP and PD (APPD); and AP and PD with treatment (APPDt). AP and PD lesions were induced for four weeks. Four weeks after treatments, the animals were euthanatized, and the aorta and liver were dissected for histological evaluation. For the comparison of the thickness of the aorta between groups, the Kruskal-Wallis test was used, followed by the Mann-Whitney test. For the analysis of other variables related to the aorta and liver outcomes, logistic regression was carried out.

RESULTS

Both PD and AP were associated with the development of histological alterations in the aortic arch, with no significant difference between obese and non-obese animals (p = .17). The aorta thickness was increased significantly (p < .05) with the combination of PD and AP in obese rats (APPDt-c group) compared with the other groups (NC-n, APt-n, APt-c and AP-c). The logistic regression models revealed that the untreated (OR = 7.78; 95%CI = 2.4-25) and treated (OR = 2.9; 95%CI = 1.0-8.4) groups were significantly more likely to have endothelial alterations compared with the control groups (p = .002). Obesity (OR = 16.5; 95%CI = 3.4-81.3) was the only predictor variable of liver steatosis (p < .001).

CONCLUSION

Histological alterations in the aortic arch of obese and non-obese rats were observed in the presence of periodontal disease and apical periodontitis. The combination of PD and AP increased the aorta thickness in obese rats. A reduction of vascular endothelial lesions was observed with the treatments of PD and AP.

Three-dimensional pattern of inflammatory periapical lesion extension in the premolar's region: an application of K-means clustering

BACKGROUND

Cone-beam computed tomography (CBCT) provides better diagnosis of endodontic lesions.

INTRODUCTION

The present study would assess the pattern of periapical lesion extension in premolar teeth using CBCT.

METHOD

In this descriptive study' 330 roots in the regions of maxillary and mandibular premolars have been evaluated. Maximum periapical lesion extensions in the three orthogonal planes (axial, coronal and sagittal) were measured and recorded in millimeters. Measurements were compared based on gender' dental arch, tooth type and root. Statistical analysis was performed using repeated measure ANOVA, Bonferroni, Chi-square tests and clustering data analysis (K-means method). The significant level was set at 0.05.

RESULT

There were significant differences between the lesion expansions in the three dimensional planes (p-value<0.001). The highest average of lesion extension in the premolar regions of the examined population was reported in the vertical dimension (4.1± 1.3), followed by horizontal buccolingual dimension (3.4±1.1) and horizontal mesiodistal dimension (3.1±1.0) respectively. According to independent variables, in the premolar region only tooth roots showed significant differences in the lesion extension (p-value=0.002). Clustering data analysis showed that the majority of the participants categorized in a cluster with lower lesion extension. Based on clustering data analysis, the small lesions were significantly observed in the first premolar and buccal roots.

CONCLUSION

Since the periapical lesion extension in the buccolingual dimension, which could not be detected in the 2-D imaging techniques, was rather high in the region of premolar teeth, CBCT -as a 3-D imaging technique- is a suitable option for the precise evaluation of periapical lesion extension. Also, the majority of the lesions in this tooth area are small and located in the buccal roots.

Wnt antagonist secreted frizzled-related protein I (sFRP1) may be involved in the osteogenic differentiation of periodontal ligament cells in chronic apical periodontitis

AIM

To explore the mechanism of secreted frizzled-related protein I (sFRP1) involvement in the osteogenic differentiation of human periodontal ligament cells (hPDLCs) under inflammatory conditions.

METHODOLOGY

hPDLCs were cultured in an osteogenic differentiation-inducing medium (odi) and subjected to the stimulation of Porphyromonas gingivalis lipopolysaccharide (P. gingivalis LPS) with or without the inhibition of sFRP1. Quantitative real-time polymerase chain reaction, Western blot and enzyme-linked immunosorbent assay were carried out to evaluate the expression of osteogenic markers as well as the classic Wnt signalling pathway. Periapical periodontitis was induced in Wistar rats to further confirm the effect of sFRP1 inhibitor on bone loss in vivo. After the Shapiro-Wilk normality test, data were analysed by Student's paired t-test or one-way Anova test with a P value less than 0.05 as the level of statistical significance.

RESULTS

Significantly decreased mRNA and protein expression of osteogenic markers were detected in hPDLCs treated with P. gingivalis LPS during osteogenic induction (P < 0.001). Increased expression of sFRP1 was observed (P < 0.01), whilst Wnt/β-catenin signalling pathway was inhibited by the addition of P. gingivalis LPS (P < 0.01). After the addition of the sFRP1 inhibitor, the decrease of osteogenic markers (P < 0.05) and the inhibition of Wnt/β-catenin signalling pathway (P < 0.05) were reversed significantly. The animal experiment further confirmed that the sFRP1 inhibitor significantly reduced bone loss of periapical lesions in vivo (P < 0.0001).

CONCLUSIONS

Wnt antagonist sFRP1 was involved in the osteogenic differentiation of hPDLCs under inflammation. Modulation of the Wnt/β-catenin signalling pathway through the inhibition of sFRP1 may offer a new perspective on the treatment of chronic apical periodontitis.

Effect of root canal debridement on inflammatory cytokine levels

In endodontic infections, inflammatory mediators such as cytokines are released, recruited and retained until the infection is eradicated. Root canal therapy is performed to prevent the spread of infection. The aim of this study was to investigate the effects of root canal debridement (cleaning and shaping) on periapical inflammation by measuring the levels of inflammatory cytokines, Interleukin-8 (IL-8) and Interleukin-10 (IL-10). The study includes twenty patients with pulp necrosis and asymptomatic apical periodontitis. Periradicular sample was collected using paper points before and after root canal debridement. Cytokine levels were determined by Sandwich Enzyme-Linked Immunosorbent Assay (ELISA). Data were analysed using paired t-test (PASW Statistics 18) (P = 0.05). All samples showed the presence of IL-8 and IL-10 prior to root canal debridement. Significantly reduced levels (P < 0.05) of IL-8 and IL-10 were detected after root canal debridement. In conclusion, root canal debridement significantly decreased the levels of the tested pro- and anti-inflammatory cytokine in the periradicular interstitial fluid.

Capsaicin-sensitive Innervation Modulates the Development of Apical Periodontitis

INTRODUCTION

Nociceptive neurons play a critical role in the detection of stimuli evoking actual or potential tissue injury. In addition, they are involved in neurogenic inflammation by the peripheral release of neuropeptides such as calcitonin gene-related peptide (CGRP). The dental pulp and periradicular tissues are innervated by capsaicin-sensitive neurons known to release CGRP. However, the role of these capsaicin-sensitive neurons in the development of apical periodontitis is largely unknown. The aim of this study was to evaluate the contribution of peptidergic neurons to the development of apical periodontitis.

METHODS

Neonatal Sprague-Dawley rats were injected with vehicle (control group) or a single subcutaneous capsaicin dose to cause the selective ablation of peptidergic neurons (neonatal capsaicin group). Ablation of capsaicin-sensitive neurons was verified with confocal microscopy, capsaicin-induced eye-wipe nocifensive behavior test, and by measurement of immunoreactive CGRP levels in the dental pulp. Five weeks after ablation, standardized pulp exposures were made in the mandibular left first molars. Mandibles were harvested at 7, 14, 21, and 28 days after pulp exposure and imaged with micro-computed tomography (μCT) to quantify apical lesion volume. Data were analyzed by using 2-way ANOVA analysis with Bonferroni post hoc test.

RESULTS

Rats in the control group displayed a robust capsaicin-induced nocifensive behavior, which was nearly abolished in the neonatal capsaicin group. In addition, the neonatal capsaicin group showed a significant depletion of susceptible neurons and CGRP in the dental pulp compared with control. Importantly, micro-computed tomography analysis showed larger periradicular lesions at 7 and 14 days after pulp exposure in the neonatal capsaicin group when compared with control.

CONCLUSIONS

Results identify a protective role for capsaicin-sensitive neurons in the initial phase of apical periodontitis. Thus, interventions or disorders that alter activity of capsaicin-sensitive fibers are likely to alter the development of apical periodontitis.

Cellular Profile and Expression of Immunologic Markers in Chronic Apical Periodontitis from HIV-infected Patients Undergoing Highly Active Antiretroviral Therapy

INTRODUCTION

This study tested the hypothesis that the inflammatory cell profile (CD3-, CD4-, CD8-, CD20-, and CD68-positive cells) and the expression of immunologic markers (tumor necrosis factor α, interferon-γ, interleukin-6, and interleukin-18) in chronic apical periodontitis are the same between non-HIV-infected patients and HIV-infected patients undergoing highly active antiretroviral therapy (HAART).

METHODS

Thirty-four surgically excised chronic apical periodontitis lesions were sampled from 34 patients (17 HIV-infected and 17 non-HIV-infected). The lesions were extracted from teeth with no previous endodontic treatment. All HIV-infected patients were undergoing HAART. The specimens were submitted to histopathologic and immunohistochemical analyses by using an optical microscope. Immunoexpression was graded into 2 levels, focal to weak and moderate to strong. The χ(2), Fisher exact, and Mann-Whitney tests were used to analyze all significant differences between groups.

RESULTS

Periapical cysts represented 70.6% and 52.9% of the lesions in the HIV-infected and non-HIV-infected groups, respectively; however, no statistically significant difference was observed (P = .481). There were no statistically significant differences between groups for the inflammatory cell profile and for any of the immunologic markers (P > .05).

CONCLUSIONS

There are no statistically significant differences of the cellular profile and expression of immunologic markers in chronic apical periodontitis between non-HIV-infected patients and HIV-infected patients undergoing HAART.

ST2 deletion increases inflammatory bone destruction in experimentally induced periapical lesions in mice

INTRODUCTION

ST2 is a member of the interleukin (IL)-1 receptor family, and IL-33 is its natural ligand. ST2 signaling promotes Th2 immune response in allergy, autoimmunity, and chronic inflammatory disorders, but its role in the pathogenesis of periapical lesions is unknown. The purpose of this study was to investigate whether ST2 gene deletion affects the development of experimentally induced periapical lesions in mice.

METHODS

Pulps of mandibular molars from wild-type (WT) and ST2 knockout (ST2(-)/(-)) BALB/c mice were exposed and left open to the oral environment. After death, hemi-mandibles were isolated and prepared for histologic, immunohistochemical, and flow cytometric analysis.

RESULTS

The expression of IL-33 and its receptor ST2 was higher in periapical lesions in WT mice compared with normal root apices (both P < .05). The increased periapical bone loss observed in ST2(-)/(-) mice was associated with enhanced influx of neutrophils, CD3+ CXCR3+ Th1 cells, and CD3+ CCR6+ Th17 cells and increased number of tartrate-resistant acid phosphatase+ osteoclasts (all P < .05). Furthermore, periapical lesions in ST2(-)/(-) mice contained increased percentages of T cells expressing interferon-γ, IL-17, tumor necrosis factor-α, and IL-6 (all P < .05). In comparison with WT mice, CD3+ receptor activator of nuclear factor kappa B ligand+ T cells were increased, whereas CD3+ osteoprotegerin+ T cells were decreased in the lesions of ST2(-)/(-) mice (both P < .05).

CONCLUSIONS

ST2 deletion increases inflammatory bone loss in experimental periapical lesions in mice, which is associated with enhanced Th1/Th17 cell mediated periapical immune responses and increased osteoclastogenesis.

Promotion of endodontic lesions in rats by a novel extraradicular biofilm model using obturation materials

Although extraradicular biofilm formation is related to refractory periapical periodontitis, the mechanism of extraradicular biofilm development, as well as its effect on periapical lesions, is unknown. Therefore, we aimed to develop an in vivo extraradicular biofilm model in rats and to identify and quantify extraradicular biofilm-forming bacteria while investigating the effect of extraradicular biofilms on periapical lesions. Periapical lesions were induced by exposing the pulpal tissue of the mandibular first molars of male Wistar rats to their oral environment. Four weeks later, gutta-percha points were excessively inserted into the mesial root canals of the right first molars (experimental sites) but not the left first molars (control sites). After 6 and 8 weeks of pulp exposure, the presence of extraradicular biofilms was confirmed histomorphologically, and biofilm-forming bacteria were identified by using classical culture methods. The biofilms were observed in the extraradicular area of the experimental sites. Similar species were detected both inside and outside the root canals. The bacterial count, quantified by real-time PCR assays, in the extraradicular area gradually increased in the experimental sites until 20 weeks after pulp exposure. After 8 weeks of pulp exposure, the periapical lesion volume that was measured by micro-computed tomography was significantly larger in the experimental sites than in the control sites (P < 0.05 by Welch's t test). These results suggest that we developed an extraradicular biofilm model in rats and that extraradicular biofilms affect developing periapical lesions.

Vascular endothelial growth factors and receptors are up-regulated during development of apical periodontitis

INTRODUCTION

Apical periodontitis is a common inflammatory disease caused by persistent root canal infection and is characterized by bone resorption. Vascular endothelial growth factors (VEGFs) and their receptors (VEGFRs) have been described in many pathologic and inflammatory conditions, but their involvement in the development of apical periodontitis has not been thoroughly investigated. The aim of this study was to quantify gene expression and localize VEGF-A, VEGF-C, and VEGF-D and VEGFR-2 and VEGFR-3 in a rat model of apical periodontitis.

METHODS

Molar pulps were unilaterally exposed to the oral cavity for 10 or 21 days. Jaw sections were used for localization of VEGFs and VEGFRs with immunohistochemistry and identification of cells with double immunofluorescence. Gene expression analysis for VEGF-A, VEGF-C, and VEGFR-3 of periapical tissues was performed with quantitative real-time polymerase chain reaction.

RESULTS

All investigated factors and receptors were expressed immunohistochemically in blood vessels at the periodontal ligament of control teeth and were up-regulated during lesion development. In apical lesions, macrophages and neutrophils expressed all studied factors and receptors, with macrophages being an important source of VEGF-C and VEGF-D. Osteoclasts expressed VEGFR-2 and VEGFR-3, and the latter was also identified in fibroblast-like cells in the lesions. VEGF-A and VEGFR-3 gene expression was up-regulated at days 10 and 21 (P < .05).

CONCLUSIONS

The current findings indicate that the VEGF family and receptors are involved in vascular remodeling and immune functions during disease development. The presence of VEGFR-2 and VEGFR-3 on osteoclasts indicates that bone resorbing activity is influenced by VEGFs.

A controversial role for IL-12 in immune response and bone resorption at apical periodontal sites

Periapical lesions are inflammatory conditions of tooth periapical tissues, triggered by dental pulp infection and characterized by exudation of immune cells to the affected tissues and production of inflammatory mediators such as cytokines. The inflammatory periapical reaction is mainly driven by Th1, Th2, and Th17 responses, and such polarization may modulate progression of the disease and expression of bone proresorptive cytokines. IL-12 is a potent inducer of IFN-γ production, which stimulates Th1 effector cells. Many evidences have shown a positive correlation between the bone resorptive cytokine IL-1β and the production of IL-12 and IFN-γ. Furthermore, IL-12 may have a potential role in the release of bone resorptive mediators and blockade of Th2 cytokines, affecting the progression of periapical bone loss. Nevertheless, IL-12 and IFN-γ have also been described as suppressors of osteoclast differentiation and activation, favoring bone maintenance. This paper focuses on the controversial roles of IL-12 in periapical lesions.

Regulatory T cells in mouse periapical lesions

INTRODUCTION

T-regulatory (Treg, CD4+ FOXP3+) cells constitute a unique subpopulation of CD4+ T cells that inhibit T-cell responses and prevent disease development/exacerbation in models of autoimmunity. In the present study, we tested the hypothesis that Treg cells are induced in periapical lesions by dental pulp infection.

METHODS

In situ hybridization (ISH) was used to localize FOXP3+ cells on day 21 after pulp exposure of the first molar teeth and infection with bacteria from the oral environment. FOXP3/GFP knock-in transgenic mice were used to quantify FOXP3+ Treg cells that infiltrate into periapical lesions by flow cytometry on days 7, 14, and 21 after infection. Periodontal ligament from uninfected teeth served as a negative control.

RESULTS

ISH showed strong signals that showed the presence of FOXP3+ cells mainly at the periphery of periapical lesions. In contrast, no positive cells were present in the periodontal ligament of uninfected controls. Flow cytometry showed an increase in the number of FOXP3+ Treg beginning between day 7 and day 14 (0.69% of the infiltrate) after infection and increased to day 21 (0.94%) (p < 0.05 and p < 0.001, respectively, vs uninfected controls). Treg were also increased in number in draining cervical lymph nodes after pulpal infection.

CONCLUSIONS

These results show that Treg cells are induced to infiltrate into periapical lesions by pulpal infection and suggest that they increase in a time-dependent manner.

The influence of mineral trioxide aggregate on adaptive immune responses to endodontic pathogens in mice

This study assessed the influence of mineral trioxide aggregate (MTA) on adaptive immune responses. BALB/c mice were immunized with heat-killed Fusobacterium nucleatum (Fn) in MTA or other control adjuvants, and serum IgG responses to Fn were measured. Either Fn- or Peptostreptococcus anaerobius (Pa)-reactive memory T cells (Tm) were preincubated in vitro with/without MTA and restimulated with Fn or Pa. Tm proliferation and cytokine production were assessed. Compared with control groups, immunoglobulin G-antibody responses were upregulated in mice immunized with Fn in MTA in a similar manner to animals immunized with Fn in Freund's adjuvant or aluminum hydroxide adjuvant. Although MTA did not affect the upregulated expression of interleukin 10, tumor necrosis factor alpha, or RANKL by Tm, it suppressed the proliferation of Pa- or Fn-Tm and inhibited their production of Th1- or Th2-signature cytokines. MTA upregulated the adaptive humoral immune responses but had little or no effect on pro- or anti-inflammatory cytokine production by Tm.

Receptor activator NFkappaB-ligand and osteoprotegerin protein expression in human periapical cysts and granulomas

OBJECTIVE

The purpose of this study was to determine the expression of receptor activator of NFkappaB ligand (RANKL) and osteoprotegerin (OPG) associated with bone destruction in periapical cysts and granulomas.

STUDY DESIGN

Forty human dental chronic periapical lesions were collected after periapical surgery. The lesions collected were fixed in 10% buffered formalin and histologically processed. At least 2 sections of each specimen were stained with hematoxylin and eosin for microscopic diagnosis. After that, 10 human periapical granulomas and 10 cysts were selected for immunohistochemical analysis for RANKL, OPG, and CD68+.

RESULTS

Polymorphonuclear neutrophils, macrophages, endothelial cells, and lymphocytes were stained for RANKL and OPG in both lesions. Epithelial cells were also stained for RANKL and OPG in periapical cysts. Quantitative analysis was conducted and the results were expressed as a ratio of the number of immunostained cells over the total number of cells in the field (n = 100). The ratio of RANKL+/total cells was higher than OPG+/total cells in periapical granulomas (0.553 +/- 0.153 and 0.483 +/- 0.189, respectively; P < .0012; paired t test) and in cysts (0.519 +/- 0.09 and 0.339 +/- 0.117, respectively; P < .0001; paired t test). The ratios of OPG+/total cells (P < .0001; paired t test) and RANKL+/total cells (P < .0322; paired t test) were greater in granulomas than in cysts. However, the ratio RANKL+/OPG+ in granulomas (1.336 +/- 0.723) and cysts (1.404 +/- 0.385) was not significantly different. The ratio of CD68+/total cells was significantly higher in granulomas (0.381 +/- 0.040) than in cysts (0.307 +/- 0.068) (P < .0001; unpaired t test with Welch correction).

CONCLUSION

Taking into account the limitations of the experimental approach employed, our findings indicate the presence of RANKL and OPG in cysts and granulomas, strongly suggesting the involvement of these gene products in the development of periapical lesions.

Role of IL-2 and Helper T-Lymphocytes in Limiting Periapical Pathosis

The purpose of this study was to examine the role of IL-2 and helper T-lymphocytes in the development of periradicular lesions in rats. In control animals, periradicular lesions developed within 28 days following pulpal infection. Immunologically, some anti IL-2 and anti CD4-reactive helper T-lymphocytes infiltrated the periapical tissue at 14 days, and their numbers increased at 28 days. In experimental animals, tacrolimus (FK506) was injected every day to inhibit the IL-2 production by helper T-cells. Histologically, the pulpal necrosis and periradicular inflammation in tacrolimus-treated rats were more severe than those in the control rats. Furthermore, the areas of pulpal necrosis and periradicular lesion in the immunosuppressed rat were significantly greater than those in the normal ones. The numbers of IL-2- and CD4-positive cells in the lesion of the experimental rats were statistically lower than those of the control ones. These results show that the decrease in IL-2 might have promoted the development of periradicular lesions.

Effect of mineral trioxide aggregate on cytokine production by peritoneal macrophages

AIM

To test the effect of two commercial brands of grey mineral trioxide aggregate (ProRoot and MTA-Angelus) on cytokine production by M1 and M2 inflammatory macrophages.

METHODOLOGY

M1 (from C57BL/6 mice) and M2 peritoneal inflammatory macrophages (from C57BL/6 IL12p40-/- mice) were obtained and cultured in vitro in the presence of MTA. The cellular viability and the production of tumour necrosis factor-alpha, interleukin (IL)-12 and IL-10 in response to stimulation with interferon-gamma and Fusobacterium nucleatum or Peptostreptococcus anaerobius were evaluated. Data were analysed by Mann-Whitney, Kruskal-Wallis and anova tests.

RESULTS

The cements did not interfere with cellular viability or with cytokine production by either type of macrophage. However, M2 macrophages produced higher levels of IL-10 when stimulated with F. nucleatum than M1 macrophages (P < 0.05).

CONCLUSIONS

The brands of MTA evaluated did not interfere in the cytokine response by M1 or M2 macrophages to the two bacteria tested. However, a difference in cytokine production between the two types of macrophages was found.

Effect of root canal dressings on the regeneration of inflamed periapical tissue

The aim of this study was to evaluate the effects of chlorhexidine and calcium hydroxide on apical periodontitis in rats. Experimentally induced apical periodontitis was established on the mesial roots of maxillary molars of Wistar rats by leaving the root canals exposed to the oral cavity for 14 d. In the positive control group (n=10 teeth), the root canals were not further treated, but the coronal access openings were filled with composite. In the negative control group (n=10 teeth), partial pulpotomies were performed aseptically and the coronal access openings were sealed immediately. In a third control group (n=10 teeth) the canals were instrumented, left empty, and the coronal access openings were sealed. In the experimental groups, the root canals were instrumented and filled with either 2% chlorhexidine gel or calcium hydroxide paste (n=10 teeth per group). After 7 d all rats were killed and the histological sections were stained for microscopic analysis of periapical regeneration. The data of the subjective evaluation were analyzed with the Kruskal-Wallis test. Lesion sizes were measured and statistically analyzed using the ANOVA and post-hoc Scheffé test. The two treatment groups showed significantly lower average inflammatory scores and smaller lesion sizes than the positive and third control group (p<0.05). No statistically significant differences were obtained between the two treatment groups (p>0.05). Chlorhexidine used as an intra-canal medicament showed good periapical regeneration, suggesting that this may be an alternative to calcium hydroxide root canal dressing.

Cytokine production in response to endodontic infection in germ-free mice

This study evaluated the cytokine profiles (type 1 or type 2) that are triggered by and modulate endodontic periapical infections in the root canal system of germ-free mice. Microorganisms isolated from two patients with pulpal necrosis were inoculated into two groups of experimental animals: group I (Gemella morbillorum) and group II (Bifidobacterium adolescentis, Fusobacterium nucleatum and Clostridium butyricum). In vitro, G. morbillorum induced type 1 cytokine synthesis, while the modulation processed in vivo seemed to have the opposite effect, with a reduction in the basal levels of IL-12 and IFN-gamma, IL-4-independent down-modulation. In vitro, microorganisms from group II, in poly-infection, induced a reduction of type 1 cytokine levels from day 10 to day 20, which seemed to be modulated via IL-4. In vivo, however, a predominance of the immune response to one species over the others occurred.

Pathologic interactions in pulpal and periodontal tissues

Both endodontic and periodontal disease are caused by a mixed anaerobic infection. The pathways for the spread of bacteria between pulpal and periodontal tissues have been discussed with controversy. This article is an attempt to provide a rational approach to the perio-endo/endo-perio question based on a review of the relevant literature. In the light of evidence, clinical concepts for the diagnosis and treatment of lesions involving both periodontal and pulpal tissues are discussed.

Endoperiodontal lesion. A case report

The purpose of this case report is to present an unusual endoperiodontal lesion on tooth 46 in an 8-year-old child. The absence of any carious process and the presence of the typical radiographic aspect of an infrabony defect, led us to consider the periodontal aetiopathogenesis. In spite of all this, an accurate periodontal probing of all the teeth and the use of the pulp tester for teeth 46 and 36 led us to diagnose properly a truly endodontic lesion. The endodontic treatment of the involved tooth achieved the complete healing of the lesion.

A mouse model of inflammatory root resorption induced by pulpal infection

OBJECTIVE

The present study was undertaken to determine the frequency and extent of apical root resorption associated with induced periradicular lesions in mice.

STUDY DESIGN

Bone and root resorption was quantified by using two- and three-dimensional micro-computed tomography (mu-CT) in the lower first molars of mice subjected to pulp exposure and infection.

RESULTS

mu-CT measurements showed significant apical resorption in exposed and infected teeth, resulting in an average distal root shortening of 12.7% (P <.001 vs unexposed). These findings were confirmed with three-dimensional reconstituted images that showed thinning and shortening of the distal root. Tartrate-resistant acid phosphatase clastic cells were associated with resorption lacunae on the cementum of root apices, as well as on bone at the periphery of the periradicular lesions. Brown and Brenn staining showed the presence of bacteria in dentinal tubules adjacent to resorbed cementum.

CONCLUSIONS

Apical root resorption is a prominent and consistent finding associated with periradicular infection in the mouse. This species represents a convenient model for studying the pathogenesis of inflammatory root resorption in vivo.

Implantation of bacteria from human pulpal necrosis and translocation from root canals in gnotobiotic mice

The aim of this study was to determine whether microorganisms recovered from infected human root canals were able to survive and translocate to a local lymph node when experimentally inoculated into the root canal system of germ-free mice. The microorganisms isolated from two patients with pulpal necrosis were inoculated in two groups of experimental animals; group I (Gemella morbillorum) and group II (Bifidobacterium adolescentis, Fusobacterium nucleatum, and Clostridium butyricum). G. morbillorum showed the highest frequency of colonization and translocation to the draining lymph node. In group II only F. nucleatum and C. butyricum colonized and translocated when inoculated in tri-association. When the bacteria from group II were inoculated in monoinfection all three species colonized the root canal of germ-free mice and translocated to the draining lymph node, but with different frequencies. We conclude that selective mechanisms occur in which some bacterial species are fit to survive, multiply, and translocate in the germ-free mouse model.

Protective and destructive immune reactions in apical periodontitis

Apical periodontitis is initiated primarily by the mixed microflora of infected root canals. Continuous flow of bacteria and their products through the apical foramen induces influx, activation and coordinated interaction of immune-inflammatory cells within the periapical area. Successful mobilization of host defense mechanisms prevents abundant extraradicular bacterial invasion. However, anti-infective effector mechanisms are not restricted to killing the invading microorganisms but also destroy normal tissue components and induce bone absorption, resulting ultimately in the loss of the affected teeth. Moreover, autocrine and paracrine loops of stimulation may lead to the perpetuation of the local inflammatory lesion and may also alter the function of remote tissues and organs. This review attempts to summarize current knowledge about the pathogenic mechanism of apical periodontitis, focusing on the formation of a special granulation tissue that effectively fights bacteria originated from the infected pulp chamber and, by exerting this protective function, also contributes to harmful local and distant events. The dynamic equilibrium between defensive and destructive mechanisms may provide a pathobiological basis for better understanding of clinical signs and symptoms of various forms of apical periodontitis lesions and influence treatment strategy and practice.

Quantification of periapical bone destruction in mice by micro-computed tomography

Bacterial infections of the dental pulp result in tissue destruction and periapical bone resorption. The availability of genetically engineered mouse strains is a major advantage in the use of this model system for studies of periapical pathogenesis. The main limitation of the mouse model is its small size, and the necessity for laborious histologic analyses to quantify periapical bone destruction. In the present study, we evaluated the use of a new technology, high-resolution micro-computed tomography (micro-CT), for the rapid and non-invasive quantification of periapical bone destruction. Periapical lesions were induced in the lower first molars of mice by exposing the pulp to the oral environment. Mandibles were harvested on day 21 after pulp exposure, and were subjected to micro-CT analysis, with 17-microm-thick radiographic sections. Samples were then decalcified, embedded, and sectioned for histology. The cross-sectional area of periapical lesions was determined by image analysis of corresponding micro-CT and histologic sections. The results showed a highly significant correlation between micro-CT and histology (p < 0.0001), with mean differences of 4. 1% (range, 0.9 to 7.2%) between the two methods. The mean error associated with image analysis was 4.9% for images obtained by both micro-CT and histology. The variability of replicate (n = 5) independent micro-CT determinations was 3.4%, less than that associated with the image analysis error. These results demonstrate that micro-CT imaging is a rapid, reproducible, and non-invasive method, that gives results that are closely comparable with those obtained by histology. Micro-CT appears to have utility for the accurate quantification of changes in bone architecture in small biological specimens.

Expression of bone-resorptive and regulatory cytokines in murine periapical inflammation

Periapical bone destruction earlier was shown to be mediated primarily by interleukin (IL)-1alpha in a rat model. The production and action of IL-1alpha is in turn potentially modulated by a network of cytokines, which are produced by infiltrating T-helper type 1 (Th1) and type 2 (Th2) lymphocytes, and resident connective tissue cells within the lesion. This study was designed to examine the kinetics of expression of 10 cytokines in experimentally induced murine periapical lesions, including bone-resorptive [IL-1alpha, tumour necrosis factor alpha (TNFalpha), IL-6, IL-11], Th1-type [IL-2, IL-12, interferon-gamma (IFNgamma)] and Th2-type (IL-4, IL-6, IL-10, IL-13) mediators. Cytokine mRNA expression was assessed qualitatively by reverse transcription-polymerase chain reaction, and cytokine proteins quantified by enzyme-linked immunosorbent assay. IL-1alpha and TNFalpha protein and mRNA were highly expressed, beginning on day 7, and increased to day 28. IL-6 increased to day 14 and then declined, whereas the expression of IL-11 was not modulated by pulp exposure. Most of the Th1-type cytokines, including IL-2, IL-12, and IFNgamma, showed an increase in mRNA and/or protein expression in periapical lesions after pulpal exposure; the expression of Th2-type cytokines was similarly increased, but had declined at the latest time-point (day 28), suggesting possible inhibition by Th1-type mediators. Significant correlations were observed between levels of IL-1alpha and Th1-derived pro-inflammatory mediators IL-2, IL-12, TNFalpha, and IFNgamma. There was a lack of correlation between IL-1alpha and Th2-type anti-inflammatory mediators, including IL-4, -6, and -10. These results indicate that a cytokine network is activated in the periapex in response to bacterial infection, and that Th1-modulated pro-inflammatory pathways may predominate during periapical bone destruction.

Periapical inflammatory responses and their modulation

Periapical inflammatory responses occur as a consequence of bacterial infection of the dental pulp, as a result of caries, trauma, or iatrogenic insult. Periapical inflammation stimulates the formation of granulomas and cysts, with the destruction of bone. These inflammatory responses are complex and consist of diverse elements. Immediate-type responses--including vasodilatation, increased vascular permeability, and leukocyte extravasation--are mediated by endogenous mediators, including prostanoids, kinins, and neuropeptides. Non-specific immune responses--including polymorphonuclear leukocyte and monocyte migration and activation, and cytokine production--are elicited in response to bacteria and their products. Interleukin-1 and prostaglandins in particular have been implicated as central mediators of periapical bone resorption. Chronic periapical inflammation further involves specific T- and B-cell-mediated anti-bacterial responses, and activates a network of regulatory cytokines which are produced by Th1- and Th2-type T-lymphocytes. Various naturally occurring and genetically engineered models of immunodeficiency are beginning to help elucidate those components of the immune system which protect the pulpal/periapical complex. Both specific and non-specific responses interface with and are regulated by the neural system. The modulation of these responses by immune response modifies, cytokine antagonists, and other novel therapeutic agents is discussed. As an experimental model, periapical inflammation has many advantages which permit it to be used in studies of microbial ecology and pathogenesis, host response, neuroimmunology, and bone resorption and regeneration.

Experimental chronic infection induced in mice by Actinomyces israelii entrapped in alginate gel

Tissue responses to experimentally induced actinomycotic lesions were investigated in mice by both light and transmission electron microscopy. Micro-organisms of Actinomyces israelii were entrapped in alginate gel and injected into the subcutaneous tissue over the periosteum of the mouse cranium. One day after the injection (initial stage), a non-stained amorphous structure was located in the core of the lesion, corresponding to the injected gel with bacteria. Numerous neutrophils surrounded the core region and phagocytized the injected complex actively. At days 3-7 (intermediate stage), the lesion became well developed. The core structure became eosinophilic and separated to form island-like structures. No lesion was recognized in the control group (gel without bacteria) until day 14. After 30 days (late stage), the lesions displayed more static features, similar to the "sulphur granules" characteristic of actinomycotic lesions. At the late stage, foamy cells increased in number and took the place of neutrophils in the alginate islands. By transmission electron microscopy these foamy cells were seen to be filled with lysosomal vesicles containing electron-dense foreign material. Thus, these cells appeared to be macrophages that had phagocytized degenerated neutrophils containing bacteria. Along with the active phagocytosis by foamy cells that progressed in the late stage, a collagenous capsule became conspicuous and separated the lesion from the intact tissue. The bacteria remained in the gel islands until at least day 60, although they considerably decreased in number with time. Serum IgG antibody titres began to rise within 24 h of the injection, reached a peak concentration at day 14 and remained a significantly high (p < 0.01, vs 0 time) until day 120. These results suggest that this animal model is useful for inducing experimental chronic infectious lesions.

Development of periradicular lesions in immunosuppressed rats

PROBLEM

The role of bacteria has been well established in pulpal and periapical diseases, but the contribution of the host defenses is less clear.

OBJECTIVES

The purpose of this study was to compare periradicular lesion development in immunosuppressed rats with that in normal rats.

STUDY DESIGN

Fifteen rats were given weekly injections of Cytoxan (Bristol Laboratories) to suppress their immune systems. The pulps of mandibular first molars of these animals and another 15 rats that had received no medications were exposed and left open to their oral flora. The rats were killed at 2, 4, and 6 weeks. Radiographic analysis was performed by means of a computer linked to a digitizing board and stylus. In addition, specimens were decalcified, sectioned, stained, and examined under a microscope with a grid to quantify relative percentages of surface areas of bone, root, periodontal ligament, marrow spaces, soft tissue, and inflammatory infiltrate.

RESULTS

Statistical analysis showed a significantly greater radiographic bone loss in the immunosuppressed group only at 4 weeks. No significant histologic differences were found between the two groups.

CONCLUSION

Our results suggest that reduction of circulating leukocytes may not significantly affect the development of periradicular pathosis in rats.

Contemporary endodontology

Clinical endodontics has made significant progress during this century. This lecture will critically review the major breakthroughs that have taken place during this period. The final judgement of the value of this progress, however, is the quality of care we can deliver to our patients. Although the advances have been impressive, there are also major disappointments and problems that need to be recognised. Looking at clinical endodontics today, there is clearly a dissonance between sound scientific knowledge and empirical clinical practice. It is important that these problems are recognised and that endodontic research and teaching are refocused. Only by decisive action can progress be assured for clinical endodontics and the prospect will be bright.

IL-1 alpha and TNF-alpha expression in early periapical lesions of normal and immunodeficient mice

T-helper and B-lymphocytes may contribute to mechanisms that result in bone-resorptive cytokine production in periapical lesion. Mice with severe combined immunodeficiency (scid) lack functional B- and T-cell immunity. The purpose of this study was to investigate the progression of pulp necrosis and the histomorphometric features of periapical lesions in scid vs. normal mice. The expression of the bone-resorptive cytokines IL-1 alpha and TNF-alpha was also investigated. Sixteen five-week-old homozygous scid mice and 14 normal BALB/cJ mice were used. The pulps of mandibular first molars were exposed for 1, 2, 3, or 4 weeks. Blocks of tissue containing the mandibular teeth and supporting structures were processed for both light microscopic examination and immunohistochemical staining for IL-1 alpha dna TNF-alpha. Central sections were randomized, their images were blindly digitized into a computer, and the areas of the lesions surrounding the distal root apices were measured. The cells that stained positively for the cytokines in the same area of adjacent sections were counted. Pulp necrosis progressed at similar rates in teeth from both strains. A progressive and significant increase in the periapical lesion size in both strains was observed. The scid mice lesions were significantly smaller than the controls at only the three-week period. There was heavy cytokine staining in periapical lesions from both strains, especially in areas that contained a mixed inflammatory infiltrate or fibroblasts. The number of positively staining cells was proportional to the lesion size. Therefore, pulpal and periapical pathosis were independent of the presence of functional T- and B-cells in this model.

Oral bone loss is increased in ovariectomized rats

Alveolar bone loss associated with periodontal disease occurs frequently in postmenopausal females, the same group that is predisposed to osteoporosis. To determine if the estrogen-deficient state enhances oral bone loss, we studied ovariectomized rats administered the potent bone-resorbing cytokine interleukin-1 or the periodontal pathogen Campylobacter rectus lipopolysaccharide (LPS). Distal root canals of first mandibular molars were instrumented with endodontic files, and bone resorbing factors were deposited and sealed into the root canal. Radiographs of periapical bone loss were evaluated using computer assisted image analysis to determine lesion size. Both interleukin-1 and C. rectus LPS caused a significant increase in lesion area in both ovariectomized and normal rats when compared with controls and a significant increase in ovariectomized animals compared to nonovariectomized animals receiving LPS. Using this endodontic model, we have demonstrated that estrogen deficiency results in increased oral bone loss in rats.

Bone-resorptive cytokine gene expression in periapical lesions in the rat

Periapical bone destruction is an important pathogenic sequela of pulpal infection. Recent findings from this laboratory have demonstrated that most bone-resorbing activity in extracts of rat periapical lesions can be neutralized by an anti-interleukin (IL)-1 alpha antiserum. To further clarify pathogenic mechanisms, bone-resorptive cytokine messenger RNA (mRNA) expression was analyzed in developing rat periapical lesions. The molar teeth of 20 Sprague-Dawley rats were surgically exposed and left open to permit infection from the oral environment. Total cell RNA was isolated from periapical granuloma tissue obtained on days 3, 7, 15 and 30 after exposure. mRNA for IL-1 alpha, IL-1 beta and tumor necrosis factor alpha (TNF-alpha) was amplified by reverse transcription polymerase chain reaction, and levels were approximated by comparison to the parallel amplification of the housekeeping gene glyceraldehyde phosphate dehydrogenase. IL-1 alpha and TNF-alpha mRNA were both highly expressed beginning on day 7, increased on day 15, and declined somewhat on day 30. In contrast, IL-1 beta mRNA was expressed at much lower levels, but with similar kinetics. The kinetics of steady state IL-1 alpha and TNF-alpha mRNA levels were confirmed using the quantitative RNase protection assay, whereas IL-1 beta mRNA could not be detected by this technique. IL-1 alpha mRNA-expressing cells were identified using in situ hybridization and included infiltrating macrophages, as well as resident fibroblasts, endothelial cells and osteoclasts. These results demonstrate that the IL-1 alpha and TNF-alpha genes are highly expressed in developing periapical lesions in the rat and confirm previous studies at the protein level in this model.

Immunohistochemical examination of the distribution of macrophages and CGRP-immunoreactive nerve fibers in induced rat periapical lesions

To clarify the role of calcitonin gene-related peptide (CGRP) in the development of periapical lesions, we examined the distribution of CGRP-immunoreactive (IR) nerve fibers and macrophages, and the behavior of bone tissues in experimentally induced rat periapical lesions by immunohistochemical and quantitative methods. Although no extensive changes were observed at 7 days after pulp exposure, CGRP-IR nerve fibers increased in number until 28 days with a decrease thereafter. These neural changes were closely correlated with the alteration in number of macrophages except on day 7 when macrophages were significantly increased in number as compared with control rats. Tissue repair began to take place and a decrease in number of osteoclasts was observed when the density of CGRP-IR nerve fibers reached a peak. These results suggested that there might be a close relationship between macrophages and CGRP-IR nerve fibers and that CGRP-IR nerve fibers might participate in tissue repair in experimentally induced rat periapical lesions.

Pulpal lesions in normal and cyclosporin A treated rats

The objective of this study was to examine the development of pulpal lesions in the lower molar of control and cyclosporin A (CyA) treated rats. The pulps of the first lower molars of 20 normal and 20 CyA treated rats were exposed and left open into the oral cavity. Five animals of each group were killed at 7, 14, 21, and 28 days after the pulp exposure. The specimens were sectioned sagittally at a thickness of 7 microns and stained with hematoxylin and eosin. The pulpal lesions were similar for both normal and CyA treated rats in all studied periods and the differences between both groups were not statistically significant by the Student t test at the 5% (0.05) level of significance, indicating that the immunosuppression did not alter the evolution of the inflammatory process.

Kinetics of macrophages and lymphoid cells during the development of experimentally induced periapical lesions in rat molars: a quantitative immunohistochemical study

Quantitative phenotypical analysis for macrophages and lymphoid cells was made on periapical lesions induced by making unsealed pulp exposures in rat molars. Exudative macrophages of diverse morphology were the most dominating immunocompetent cells during all experimental periods. They exhibited almost complete distribution through the periapical lesions by the onset of active lesion expansion, and their kinetics and morphology were considerably similar to Ia+ non-lymphoid cells. Lymphoid cells started to show a notable increase shortly before the onset of active lesion expansion. CD4+ lymphocytes dominated at first, whereas CD8+ lymphocytes and plasma cells were dominant when the lesion size was stabilized. These findings suggest that macrophages of heterogenous populations play essential roles in the lesion pathogenesis by acting, depending on their functional heterogeneity, as effector cells or as antigen-presenting cells that stimulate CD4+ lymphocytes to induce an immune response. Interactions between plasma cells and CD8+ lymphocytes may be related to lesion chronicity.

Immunolocalization of bone-resorptive cytokines in rat pulp and periapical lesions following surgical pulp exposure

The bone-resorptive cytokines interleukin 1 (IL-1) and tumor necrosis factor (TNF) have been implicated in the pathogenesis of many chronic inflammatory diseases, including pulpitis and apical periodontitis.To further elucidate their role in these disorders, we have identified cells that express IL-1 alpha and TNF alpha in infected pulps and in developing rat periapical lesions after surgical pulp exposure. As detected by immunohistochemistry, IL-1 alpha- and TNF alpha-positive cells were present as early as 2 days after pulp exposure in both the pulp and periapical region. The numbers of cytokine-expressing cells increased up to day 4 in the pulp and up to day 30 in the periapex. In contrast, cells expressing IL-1 beta and TNF beta, the homologous forms of these mediators, were not found in pulp or periapical lesions during this period. Cells expressing IL-1 alpha and TNF alpha were identified primarily as macrophages and fibroblasts, with occasional staining of polymorphonuclear leukocytes. Osteoblasts and osteoclasts were also positive, whereas lymphocytes were negative. In general, cytokine-expressing cells were located proximal to abscesses and the root apex. These findings demonstrate that cells that express bone-resorptive cytokines IL-1 alpha and TNF alpha are present immediately after pulp exposure in this model, which supports the hypothesis that these mediators play a key role in pulpal and periapical pathogenesis, including the concomitant bone destruction. They also indicate that both resident connective tissue cells as well as infiltrating cells express bone-resorptive cytokines in response to infection in these lesions.

Effect of T-cell deficiency on the formation of periapical lesions in mice: histological comparison between periapical lesion formation in BALB/c and BALB/c nu/nu mice

The role of T-cells in the development of periapical lesions was investigated immunohistochemically using 16 normal (BALB/c) mice and 16 nude (BALB/c nu/nu) mice (congenitally T-cell-deficient mice). The pulp chambers of maxillar first molars of all mice were opened, and the infiltrated immunocytes (anti-Thy1.2, -Lyt-1, -Lyt-2, -L3T4, -I-Ad, -IgG, and -IgM positive cells) were determined immunohistochemically at 2, 4, 6, and 8 wk after operation. Periapical lesions appeared at 2 wk in both mouse groups. Numerous anti-I-Ad positive-stained cells appeared at 2 wk, anti-I-Ad, -Thy1.2 (-Lyt-1, -L3T4), -IgG positive-stained cells appeared between 4 and 8 wk, and periapical lesions with bone resorption rapidly increased until 4 wk in normal mice. On the other hand in nude mice, only anti-I-Ad and -IgG positive cells were present from 4 to 6 wk, and the progress of periapical lesions with inflammatory cells stopped at 6 wk. Furthermore, numerous fibroblasts were found instead of inflammatory cells at 8 wk. These findings suggest that the progression of periapical lesions with bone resorption required helper T-cells and numerous immunoglobulin-producing cells.

Reduction of infection-stimulated periapical bone resorption by the biological response modifier PGG glucan

Pulpal and periodontal diseases are bacterial infections which result in local connective tissue and bone destruction. Effective host resistance to these infections is primarily mediated by neutrophils and other phagocytic cells. PGG glucan (poly-beta 1-6-glucotriosyl-beta 1-3-glucopyranose glucan) is a biological response modifier which stimulates the production of neutrophils and upregulates their phagocytic and bactericidal activity. In the present studies, the effect of PGG glucan on infection-stimulated alveolar bone resorption was tested in an in vivo model. Periapical bone resorption was induced in Sprague-Dawley rats by surgical pulp exposure and subsequent infection from the oral environment. Animals were administered PGG glucan (0.5 mg/kg) or saline (control) subcutaneously the day before and on days 2, 4, 6, 9, 11, 13, 16, and 18 following the pulp exposure procedure. PGG glucan enhanced the number of circulating neutrophils and monocytes and increased neutrophil phagocytic activity approximately two-fold. PGG glucan-treated animals had significantly less infection-stimulated periapical bone resorption than control animals, as determined radiographically (-48.0%; p < 0.001) and by histomorphometry (-40.8% and -42.4% for first and second molars, respectively; p < 0.001). PGG glucan-treated animals also had less soft tissue destruction, as indicated by decreased pulpal necrosis. Only 3.3% of the first molar pulps from PGG glucan-treated animals exhibited complete necrosis, as compared with 40.6% of pulps from controls. Finally, PGG glucan had no effect on either PTH- or IL-1-stimulated bone resorption in vitro.(ABSTRACT TRUNCATED AT 250 WORDS)

Distribution of injected dexamethasone from the buccal vestibule of the rat mandible

Thirty-six Sprague-Dawley rats were divided into three groups of 12. Group 1 was a control, whereas group 2 had the dental pulp of the first mandibular molar acutely exposed, and group 3 had dental pulp exposure for 10 days. All animals were injected with 125I-labeled dexamethasone phosphate into the right mandibular vestibule. Each group of 12 was divided into subgroups of 4 and sacrificed at 1, 2, or 4 h. The soft tissue on the buccal side and the mandible with the molars were collected and the radioactivity determined. Dexamethasone was absorbed from the injection site and distributed to the ipsilateral mandible and to the contralateral muscle and bone similarly, regardless of the treatment. Results also indicate a possible osseous affinity for this steroid, which could be beneficial in relieving the pain of intraosseous endodontic flare-ups.

Pathogenesis of induced rat periapical lesions

Studies of the mechanisms of pathogenesis of periapical lesions were undertaken using a rat model of surgical pulp exposure. In this model, periapical lesions develop rapidly between days 0 and 15 (active phase) and more slowly thereafter (chronic phase). A Gram-negative anaerobic flora, similar to that seen in human beings, are quickly established. Lesions contain a mixed inflammatory cell infiltrate consisting of T cells, neutrophils, B cells, macrophages, and plasma cells. Helper T cells predominate during the active phase, whereas suppressor T cells are more frequent in the chronic phase. Extracts of periapical lesions contain bone-resorbing activity, the highest levels of which are present when lesions are actively expanding. Most bone-resorbing activity is mediated by the cytokine interleukin-1 alpha, as determined by biochemical criteria and antibody neutralization studies. Prostaglandin2 accounts for 10% to 15% of resorptive activity. Cells that express interleukin-1 alpha were identified in pulp beginning on day 2 after exposure and in periapical tissue beginning on day 7, as determined by in situ hybridization and immunostaining. Macrophages, fibroblasts, neutrophils, and osteoclasts were positive for interleukin-1 alpha mRNA and protein. Cells that express tumor necrosis factor alpha were also detected, whereas cells expressing interleukin-1 beta or tumor necrosis factor beta were absent. Finally, periapical bone destruction was inhibited by 60% by treatment with interleukin-1 receptor antagonist. These studies establish a key role for interleukin-1 alpha in the pathogenesis of periapical lesions in the rat model.

Effect of methotrexate-induced neutropenia on rat periapical lesion

We investigated the effect of methotrexate-induced neutropenia on periapical lesions in rats. Periapical lesions were prepared in all animals by pulpal exposure. The animals were injected with methotrexate three times a week 4 weeks before or after the pulpal exposure. The periapical lesion of each animal was examined histologically, histometrically, and immunohistochemically. The total leukocyte count and neutrophil count in the peripheral blood decreased after the injection. The methotrexate-induced neutropenia elicited after pulpal exposure did not change the status of the periapical lesion, whereas the neutropenia before the exposure inhibited the development of the lesion. Moreover, the neutropenia before pulpal exposure resulted in an inhibition of infiltration of neutrophils into the lesion.

Changes in root canal microbiota during the development of rat periapical lesions

Periapical lesions are reproducibly induced in rats by pulp exposure and infection from the oral cavity. Lesions expand rapidly between day 7 and day 15-20 (active phase), with slowed expansion thereafter. In the present study we characterized the root canal microbiota present during the active phase of lesion development in this system. The mandibular first molars of Sprague-Dawley rats were exposed on day 0. The teeth were extracted after 7 days (n = 10 animals) and 15 days (n = 10), and the microbiota present in roots was isolated and characterized. The number of colonies isolated per tooth was similar on day 7 (1.53 +/- 0.64 colony-forming units x 10(3)) and day 15 (1.49 +/- 0.37 colony-forming units x 10(3)). No colonies were isolated from unexposed control teeth. Anaerobic bacteria increased significantly between day 7 (24.3 +/- 5.7%) and day 15 (47.3 +/- 7.5%), and the proportion of gram-negative organisms increased from day 7 (24.3 +/- 6.1) to day 15 (46.9 +/- 6.8). The predominant bacteria included, on day 7: Streptococcus and Bacteroides species; on day 15: species of Streptococcus, Bacteroides, Prevotella, Neisseria and Peptostreptococcus. Streptococcus oralis, Streptococcus mitis, Streptococcus rattus, Bacteroides pneumosintes and Bacteroides ureolyticus were frequently isolated at both points. Although approximately the same mean number of different species (approximately 3.5) was isolated per tooth on both day 7 and 15, the overall diversity of the isolates increased on day 15.(ABSTRACT TRUNCATED AT 250 WORDS)